Abstracts (first author)
Role of frequency dependent selection on the maintenance of polymorphism in aposematic organisms
The maintenance of trait polymorphisms in aposematic organisms is an evolutionary puzzle. The advantage of predator learning should drive warning signals of prey towards monomorphism, yet there are several examples of polymorphic aposematic species. Solving the riddle of polymorphism in such challenging cases would therefore represent an important contribution to our understanding of polymorphism maintenance in nature. Here, we examine the role of frequency dependent selection (FDS) on the maintenance of color polymorphism in an aposematic species. While models of frequency dependent selection are common, empirical evaluations are rare. The aposematic wood tiger moth (Parasemia plantaginis) presents two distinct male color morphs (yellow and white). Some populations have an admixture of both morphs whereas a few populations present only one of them. Research has previously shown that the more conspicuous yellow morph has a survival advantage under predation, which increases with morph frequency (i.e. positive FDS). This advantage and positive FDS should lead the yellow morph to fixation, yet this is not the case. We hypothesized that counteracting reproductive FDS (negative or positive) could maintain the polymorphism. First, we tested for reproductive FDS in the species using semi-natural enclosures set with three different frequencies of male color morphs (control, white-biased, and yellow-biased) to examine if the rare or common morph has a mating advantage. The experiment showed positive FDS in mating success for both morphs. Second, we formulated a theoretical model to test whether these results, and previous results on survival, can explain the maintenance of the observed polymorphism. The model showed that our patterns of positive frequency dependence can lead to polymorphism if considered in a spatial context, where variation in interacting ecological factors (e.g. predation), combined with a very small amount of gene flow can maintain the polymorphism.